Greens senator Sarah Hanson-Young has described the situation at Christmas Island detention facilities as "dire" after a recent visit to the island.

She told Radio 6PR one young girl had become "effectively mute" as a result of her time spent in the facility and being separated from her mother, who was also in detention but had been moved to Darwin.

Ms Hanson-Young spent four days on Christmas Island visiting detainees.

She described meeting with the four and a half year old Iranian girl and her family.

"A gorgeous little girl but she's effectively become a mute over the last few months after being in detention, she's effectively been in detention for six months."

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Ms Hanson-Young said the girl's mother was pregnant and had been sent to Darwin so she could be closer to the necessary medical facilities.

"The facilities just aren't on the island."

"Her mother was sent to Darwin three months ago and yet the rest of the family, the father and little girl, were not allowed to go."

Ms Hanson-Young said the girl's father was distressed at the impact that being detained without her mother was having on his daughter.

She said the man was a university professor who had written about the need for democracy in Iran and the family had fled after receiving death threats as a result of the man's work.

Ms Hanson said "most Australians believe that if someone is in generally in need of protection then we should give it to them" but the problem was that most people in this situation were "out of sight, out of mind" in detention where they did not have a voice.

She described the accommodation the families were in as "makeshift".

"They are dongas, or shipping containers converted into rooms surrounded by electric fences effectively," she said.

Ms Hanson-Young said as access to the public and media was highly restricted, she felt it was important for politicians to provide transparency of what was happening in the centres.

"It's a pretty dire situation for the families in particular."

Ms Hanson-Young said almost 450 children, some newborn babies, were housed in detention on Christmas Island.

She said the number of young children in these centres had increased since her previous visit 18 months ago.

"Many of these young kids have been there for six months, they are all listed to be sent to Nauru or Papua New Guinea, so the level of anxiety for these people is really growing; they are going to be imprisoned there in Christmas Island or offshore for a long, long time."

Ms Hanson-Young said locals had told her of a navy boat towing a life boat behind it on Friday.

"So they are obviously still towing boats back, boats are still trying to get here but they are pushing them back," Ms Hanson-Young said.